Sheet molding material produced by associating a layer comprising a photopolymerizable material with layers comprising thermosetting resins

ABSTRACT

A sheet molding material comprising (1) an interlayer containing a photopolymerizable resin and a photocuring agent for the photopolymerizable resin, and (2) a surface layer of a thermosetting resin containing a heat curing agent for the thermosetting resin on both surfaces of the interlayer (1); and a process for the production of the sheet molding material.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 936,551, filedAug. 24, 1978, now U.S. Pat. No. 4,214,026.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a sheet molding material of a thermosettingresin and, more particularly, to a three-layer sheet molding material,and to a process for its production.

2. Description of the Prior Art

Known conventional sheet molding materials of a thermosetting resininclude "sheet molding compounds" (hereinafter, "SMC" for brevity)obtained from a mixture of a liquid unsaturated polyester resin andglass fibers, inorganic filler, etc., which is thickened with magnesiumoxide, etc., and thin prepregs obtained by impregnating a substrate suchas paper or glass cloth with a phenolic resin or an epoxy resin.

With SMC's, it is extremely difficult to obtain a flat plate whosethickness is quite accurate because the amount of flow of the resin isgreat at the time of molding. Accordingly, a special mold is required,and only one plate can be produced at a time. In addition, glass fibersare oriented to a marked extent in the direction of the flow of theresin, and, therefore, directionality occurs in the mechanicalproperties or dimensional accuracy. Consequently, dimensional changessuch as warping (laterally) or twisting (corner to corner) tends tooccur in the cured SMC sheet. Furthermore, when a different kind of thinfilm, such as a decorative sheet, a film and a metal foil, is to belaminated on such a sheet, distortions and creases tend to occur in thethin film because the surface of the sheet is not smooth and is tacky.It is difficult, therefore, to laminate such a thin film during themolding of the sheet molding material. When the thin film is laminatedafter the sheet has been cured, adhesion of the thin film to the sheetis reduced.

In a prepreg, the resin is generally partially cured, i.e., to theB-stage, and the surface is non-tacky. With such prepregs, severalhundred sheets can be produced at a time by using a multi-stage presswhich does not require a mold or a spacer. A copper foil or the like maybe laminated, simultaneously, on the sheet and the resulting laminate isutilized as a printed circuit base board. Formation of these sheets,however, requires a lamination of five or more prepregs, and thisoperation is quite laborsome and has a poor efficiency. Furthermore,since several thin prepregs are laminated, deaeration in spaces betweenthe layers is difficult, and unacceptable products with voids or pooradhesion between the layers will be formed. Production of prepregsusually involves impregnating a base material, such as paper or cloth,with a solution of a resin composition in a solvent, usually called avarnish, and evaporating the solvent. Therefore, pollution preventionmeasures must be taken to recover the solvent and prevent itsdissipation outside the system. Since the viscosity of the varnish mustbe low in order to achieve good impregnation and to eliminate bubbles, alarge amount of inorganic filler cannot be used, the cost of productioncannot be reduced by conserving the amount of expensive resin used, andthe latitude in improving the properties is narrow. Furthermore, it isvery difficult to control the flowability of the resin in the prepregwhen the resin is in the B-stage. When a large-size flat plate, e.g.,with one side measuring 1 meter, is produced, there is a greatdifference in thickness between the central and edge portions of theplate. Hence, the area of the plate which must be trimmed off is large,and the yield of the product is low.

The present invention provides a sheet molding material of athermosetting resin useful for obtaining a flat plate, which can be usedto remove these disadvantages and on which different kinds of thin filmscan be laminated at the same time.

Some of the coinventors of the present invention found that a sheetmolding material of an unsaturated polyester resin having an uncuredsurface layer and an interlayer having an average degree of curing of atleast 50% can be press-formed without using a mold or a spacer, e.g., asdisclosed in Japanese Patent Application (OPI) No. 101276/77. Thepresent invention is an improvement over the invention disclosed inJapanese Patent Application (OPI) No. 101276/77.

SUMMARY OF THE INVENTION

An object of this invention is to provide a sheet molding material whichcan be molded to the desired thickness without using a mold, a spacer,etc., which has superior moldability using multi-stage press-forming,and which permits an increased efficiency of operation to be achieved.

Another object of this invention is to provide a structure of a sheetmolding material which has a high degree of thickness accuracy and issuitable for continuous molding, and to provide a process for theproduction thereof.

Still another object of this invention is to provide a sheet moldingmaterial on which different kinds of thin films can be laminated, andwhich can be formed into a molded sheet having a high level ofdimensional stability.

Accordingly, the present invention in one embodiment provides a sheetmolding material comprising (1) an interlayer containing aphotopolymerizable resin and a photocuring agent for thephotopolymerizable resin; and (2) a surface layer of a thermosettingresin containing a heat curing agent for the thermosetting resin on bothsurfaces of the interlayer (1).

The present invention in another embodiment provides a sheet moldingmaterial as described above in which only the interlayer (1) has beencured by irradiation with light and both surface layers (2) remain in anuncured state.

In a further embodiment, the invention provides a sheet molding materialas described above where the surface layers (2) additionally contain acontinuous-phase base material.

In an even further embodiment, the invention provides a sheet moldingmaterial as described above where a metal layer is further laminated onat least one of the surface layers (2).

In another further embodiment of the present invention, the presentinvention provides a process for continuously producing the sheetmolding material as described above, which comprises

extruding a composition containing a photopolymerizable resin and aphotocuring agent for the photopolymerizable resin as the interlayer(1), using an extruder and a sheet die,

adhering a surface layer of a thermosetting resin containing a heatcuring agent for the thermosetting resin to both surfaces of theinterlayer (1) to form surface layers (2) thereon, and

irradiating the assembly with light to cure the interlayer (1).

DETAILED DESCRIPTION OF THE INVENTION

When the sheet molding material of this invention described above isexposed to light, only the interlayer (1) containing a photocuring agentand a photopolymerizable resin is cured, and both surface layers (2)which do not contain a photocuring agent necessarily remain uncured.Thus, the sheet molding material does not require the complicatedconditions for use described in Japanese Patent Application (OPI) No.101276/77, such as the thickness of the sheet, the use of a specialphotocuring agent, the proportions of the photocuring agent, the heatcuring agent and inorganic filler, and the temperature and theconcentration of oxygen in the atmosphere at the time of photocuring.

Any combinations of photocuring agents and photopolymerizable resinswhich will be activated by light and polymerized can be used as theinterlayer (1). Other additives, for example, short fibers which are areinforcing material and serve to control flowability; inorganic fillersfor low shrinkage, cost reduction, and impact strength; fire retardants;thermosetting resins; thermoplastic resins for inhibiting shrinkage; andthickeners for flow control; can also be employed in the interlayer (1)in amounts which do not impair photocuring.

The thickness of the interlayer (1) is limited only by the ability topermit transmission of light. For example, a composition for theinterlayer which does not contain the various additives described aboveand permits a good transmission of light of the wavelength required forcuring can be formed into a layer having a thickness of up to about 30mm, more generally, 0.5 mm to 10 mm or more.

Photopolymerizable resins used in the interlayer (1) in this inventionare resins which polymerize due to the action of a photocuring agent toform a three-dimensional network structure. Suitable photopolymerizableresins which can be used include resins conventionally used as aso-called photopolymer comprising photopolymerizable prepolymers,oligomers and monomers. Suitable examples of photopolymerizable resinswhich can be used are disclosed in U.S. Pat. Nos. 2,875,047, 3,029,145,3,101,270, 2,927,022, 2,902,365, 2,046,611, 3,024,180, 2,929,710,2,972,540, 2,760,863 and 3,031,301. Suitable examples ofphotopolymerizable prepolymers, oligomers and monomers are disclosed inChem. Rev., 68, 125 (1968), G. Oster, Encyclopedia of Polymer Scienceand Technology, Vol. 10, p. 145, Interscience (1969), J. Kosar,Light-Sensitive Systems: Chemistry and Application of Non-Silver HalidePhotographic Processes, John Wiley & Sons. Inc., (1965), and G.Nagamatsu, Photosensitive Polymers, Kodansha (1977).

Specific examples of suitable photopolymerizable prepolymers oroligomers are unsaturated polyesters, epoxy resins, unsaturated epoxyresins, unsaturated polyurethanes, polyvinyl cinnamate, unsaturatedpolyvinyl alcohol, unsaturated polyamides, unsaturated silicone resins,resins resulting from the attaching of an unsaturated group to a maleicacid copolymer by an ester linkage, a ring-opening polymerizationproduct of glycidyl methacrylate, polybutadiene, and a diallyl phthalateprepolymer.

More specifically, suitable unsaturated polyesters which can be employedcomprise ester polycondensates of unsaturated acids, such as fumaricacid, maleic acid, itaconic acid, citraconic acid, and saturated acids,such as phthalic acid, isophthalic acid, terephthalic acid,endomethylenetetrahydrophthalic anhydride, adipic acid, sebacic acid,and succinic acid with glycols, such as ethylene glycol, propyleneglycol, butanediol, pentanediol, neopentyl glycol, hydrogenatedbisphenol A, etc.

Suitable epoxy resins which can be employed include epoxy resinsobtained by reaction of bisphenol A and epichlorohydrin, alicyclic epoxyresins, novolak-type epoxy resins, 1,2-polybutadiene epoxy resins, andthe like. A suitable epoxy equivalent range for these epoxy resinsranges from about 100 to about 2,000.

Suitable unsaturated epoxy resins which can be employed include resinsobtained by esterification of the above-described epoxy resins withacrylic acid or methacrylic acid.

Suitable examples of unsaturated polyurethanes which can be employedinclude those as described in Japanese Patent Application (OPI) No.27801/1973 of the formula: ##STR1## and those disclosed in JapanesePatent Publication No. 41708/1973 of the formula: ##STR2##

A suitable example of an unsaturated polyvinyl alcohol which can beemployed is disclosed in Japanese Patent Publication No. 5923/1974 ofthe formula: ##STR3## and suitable unsaturated polyamides which can beemployed include those disclosed in Japanese Patent Application (OPI)No. 115541/1974 of the formula: ##STR4##

Suitable maleic acid copolymers which can be employed include that ofthe formula: ##STR5## as disclosed in Japanese Patent Application (OPI)No. 82902/1973 and that of the formula: ##STR6## as disclosed inJapanese Patent Application (OPI) No. 37701/1974.

Suitable unsaturated silicone resins which can be employed include thosehaving therein repeating units of the formula: ##STR7## as disclosed inJapanese Printing Society Papers, 16, 131 (1976).

Specific examples of photopolymerizable monomers include monofunctionalmonomers, such as styrene, acrylonitrile, vinyl acetate,N-vinylpyrrolidone, acrylamide, acrylic acid, methacrylic acid, methylacrylate, ethyl methacrylate, butyl acrylate, cyclohexyl acrylate,benzyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate,glycidyl methacrylate, dimethyl fumarate and vinyl toluene; andpolyfunctional monomers, such as ethylene glycol diacrylate,polyethylene glycol diacrylate, diethylene glycol dimethacrylate,polyethylene glycol dimethacrylate, polypropylene glycol diacrylate,polypropylene glycol dimethacrylate, 1,4-butanediol diacrylate,1,6-hexanediol dimethacrylate, pentaerythritol diacrylate,pentaerythritol triacrylate, pentaerythritol tetraacrylate, trimethylolpropane triacrylate, trimethylol propane trimethacrylate, diglycidylphthalate dimethacrylate, a urethane compound comprising the reactionproduct of 2,4-tolulene diisocyanate and 2-hydroxyethyl methacrylate,diallyl phthalate, diallyl maleate, triallyl cyanurate, N,N-methylenebisacrylamide, cyclohexanebisacrylamide,hexahydro-1,3,5-triacryl-s-triazine, and N-acryloyl hydroxyethylmaleimide.

These photopolymerizable prepolymers or oligomers and monomers can beused either individually or as a suitable combination of two or morethereof. However, a three-dimensional structure will not be formed if amonofunctional photopolymerizable monomer is used alone, although suchwill be photopolymerized by irradiation of light. Hence, amonofunctional photopolymerizable monomer should be used in combinationwith other of the photopolymerizable materials described above.Generally, suitable combinations of photopolymerizable prepolymers oroligomers with the monofunctional photopolymerizable monomers areselected.

Photocuring agents which can be used in the interlayer (1) in thisinvention for the photopolymerizable resins are compounds which absorblight having a wavelength of at least about 200 mμ and which inducepolymerization of the photopolymerizable resin described above.Photocuring agents can be compounds which do not polymerize themselves,but are activated by absorbing light and induce polymerization. Specificexamples of the photocuring agents which can be used in this inventioninclude carbonyl containing compounds, such as benzoins, benzophenones,and nuclear quinones, e.g., benzoin, butyroin, acetoin, α-methylbenzoin,benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether,benzoin butyl ether, diacetyl benzyl benzophenone, acetophenone,4,4'-bis(dimethylamino)benzophenone, 4,4'-bis(diethylamino)benzophenone,anthraquinone, 2-methyl anthraquinone, 2-ethyl anthraquinone, 2-t-butylanthraquinone, 1-chloroanthraquinone, 1,4-naphthoquinone,9,10-phenanthraquinone, and Michler's ketone, azo compounds, such asazobenzoyl, organic sulfur compounds, mercapto compounds and disulfides,e.g., dibenzothiazolyl sulfide, decyl phenyl sulfide, diphenyldisulfide, dibenzyl disulfide, 2-mercaptobenzothiazole, thiophenol, andmethyl diethyl dithiocarbamate, halogens and halogenated compounds, e.g,bromine and carbon tetrabromide, metal carbonyls, e.g., manganesecarbonyl, inorganic compounds, e.g., tetramethyllead, tetraethyllead,zinc oxide, etc., triphenylphosphine, mixtures of the compoundsdescribed above, redox combinations such as Fe (III) and hydrogenperoxide, light-sensitive dyes, such as a combination of eosine andascorbic acid, silver bromide, etc.

A suitable amount of the photocuring agent in the interlayer (1) is anamount of at least about 0.01 part by weight, usually 0.1 to 5 parts byweight, per 100 parts by weight of the photopolymerizable resin. If theamount of the photocuring agent is less than about 0.01 part, sufficientcuring of the photopolymerizable resin in the interlayer (1) does notoccur. Amounts larger than 5 parts by weight can be used but areeconomically undesirable. Preferably, the amount of thephotopolymerizable resin in the interlayer (1) is at least about 5% byweight based on the weight of the interlayer (1). If the amount of thephotopolymerizable resin is less than about 5% by weight, control of theflowability of the resin is difficult even if the photopolymerizableresin is cured by photopolymerization. Consequently, thickness accuracyafter press-forming cannot be obtained.

Examples of short-fiber materials which can be used as an additive inthe interlayer (1) are synthetic fibers such as polyvinyl alcoholfibers, polyester fibers, acrylic fibers, polyvinyl chloride fibers,Saran (trademark of Dow Chemical) fibers, nylon fibers, andpolypropylene fibers, natural fibers such as sisal hemp and cotton,regenerated fibers such as high tenacity rayon, inorganic fibers, suchas boron fibers glass fibers asbestos fibers, and carbon fibers, metalfibers such as steel fibers, and whiskers of metals, such as Fe, Cu, Sn,Ag, of metal oxides, such as Al₂ O₃ and of carbon. In general, suitableshort-fiber materials have a length of about 3 to about 50 mm. However,after mixing and kneading with the photopolymerizable resin, a length ofabout 0.1 to 1 mm results.

Examples of inorganic fillers which can be present as an additive in theinterlayer (1) include calcium carbonate, magnesium carbonate, bariumsulfate, gypsum, alumina, aluminum hydroxide, clay, kaolin, talc, mica,silica powder, glass fiber powders (milled fibers), calcium silicate,aluminum silicate, hydrotalcite, colemanite, alum, glass beads,microspheres, fly ash, titanium dioxide, Dowsonite (trade name, producedby Alcoa), perlite, bentonite, asbestos powder, silica sand, magnesiumhydroxide, dolomite and lime. A suitable particle size for theseinorganic fillers ranges from about 0.1 to 100μ, preferably 0.5 to 20μ.Although it is only necessary for a combination of thephotopolymerizable resin and the photocuring agent described above to bepresent in the interlayer of the sheet molding material of thisinvention, generally an inorganic filler and short-fiber materials arealso employed. A suitable amount of the short-fiber material and theinorganic filler is about 5 to 30% by weight, and 10 to 80% by weight,respectively, based on the weight of the composition for the interlayer(1).

Suitable fire retardants which can be employed in the interlayer (1)include tetrabromobisphenol A, diallyl chlorendate, chlorinatedpolyethylene, antimony trioxide, tris(α-chloroethyl) phosphate,triphenyl phosphite, tetrachlorophthalic anhydride, andtetrabromobutane. These fire retardants include addition type fireretardants which are merely incorporated into the composition for theinterlayer (1) and reactive type fire retardants. A suitable amount ofthe fire retardants will depend upon the nature of the fire retardantused. More specifically, for halogen-containing fire retardants, about 8to 10% by weight based on the weight of the combustible componentspresent is suitable, for phosphorus-containing fire retardants, asuitable amount is about 5 to 6% of the combustible components presentand for antimony trioxide when used in combination with ahalogen-containing fire retardant, a suitable amount is about 0.1 to 2%by weight based on the combustible components present.

Further, some of the inorganic fillers described above can also beemployed to achieve fire retardancy, i.e., those which form carbondioxide or water at high temperatures such as Al₂ O₃ ·3H₂ O,hydrotalcite, colemanite, alum, etc. A suitable amount of theseinorganic fillers which can be used to achieve fire retardancy is about100 to 300% by weight based on the weight of the combustible componentspresent.

Suitable thermosetting resins which can be employed in combination withthe other components present in the interlayer (1) include heat curablethermosetting resins and suitable specific examples of these materialsare heat curable thermosetting resins disclosed hereinafter with respectto the thermosetting resins suitable for use in the surface layers (2).

Suitable thermoplastic resins which can be employed includemethylacrylate copolymers, polystyrene, saturated polyester,polyethylene, polypropylene and acrylonitrile copolymers. A suitableamount of these materials is up to about 5% by weight based on the totalweight of the composition for the interlayer (1).

Suitable thickeners for flow control which can be employed in thisinvention include magnesium oxide, finely divided silica (for example,Aerosil, a trademark of Nippon Aerosil Co., Ltd., SiO₂ fine powder;particle size: 8 mμ to 40 mμ), magnesium sulfate and calcium oxide.Metal crosslinking occurs when these thickeners for flow control areemployed resulting in a thickening of the compositions. A suitableamount of these thickeners which can be employed is about 0.5 to 3% byweight based on the total weight of the composition for the interlayer(1) with a suitable particle size ranging from about 0.1 to 5 microns.

When the uncured surface layers (2) are applied after the interlayer (1)has been cured by irradiation with light, care must be taken not tocause a reduction in adhesive strength between the interlayer (1) andeach surface layer (2). The composition of each surface layer (2) can beselected from a wider range of materials than the composition of theinterlayer (1), and different kinds of resins from thephotopolymerizable resins used in the interlayer (1) can be employed. Onthe other hand, when the two surface layers (2) are applied to theinterlayer (1) and then the assembly is irradiated with light, thethickness and composition of each surface layer (2) is such that thetransmission of light to the interlayer (1) for curing the polymerizableresin in the interlayer (1) is not impaired.

Suitable thermosetting resins which can be used in the surface layers(2) of the sheet molding material of the present invention includebasically any thermosetting resins, many of which are commerciallyavailable. A suitable setting temperature for the thermosetting resinswhich can be employed in this invention ranges from about 50° C. toabout 200° C. with the setting temperature being controllable by acombination of the thermosetting resin employed, the heat curing agentemployed and whether a promotor is employed.

Specific examples of thermosetting resins which can be used in thesurface layers (2) of the sheet molding material of this invention areunsaturated polyester resins, unsaturated epoxy resins, saturated epoxyresins, diallyl phthalate resins, polybutadiene, phenolic resins, andmelamine resins. These thermosetting resins can be used eitherindividually or as mixtures thereof.

The molecular weights of suitable thermosetting resins which can beemployed prior to setting can vary depending upon the nature of thethermosetting resin used. More specifically, a suitable molecular weightfor thermosetting epoxy resins ranges from about 350 to about 2,000, forunsaturated polyester thermosetting resins ranges from about 1,000 toabout 5,000, for diallyl phthalate thermosetting resins ranges fromabout 3,000 to about 20,000, for melamine thermosetting resins rangesfrom about 500 to about 2,000, and for phenolic thermosetting resinsranges from about 1,000 to about 5,000.

It is to be pointed out that unsaturated resins are described above asbeing suitable for use as thermosetting resins in the surface layers(2). Suitable unsaturated epoxy resins include the reaction products ofepoxy resins with acrylic acid and/or methacrylic acid. Morespecifically, one mol of acrylic or methacrylic acid can be additionreacted with a bisphenol-type epoxy resin having two epoxy groups in themolecule to produce the half esters thereof. When 1.5 mol of acrylicacid or methacrylic acid is reacted per mol of the epoxy group of theepoxy resin, a resin having 1.5 equivalents of unsaturated groups and0.5 equivalents of epoxy groups per molecule is obtained. Theseunsaturated epoxy resins can be polymerized either by heat or by light,but are not polymerized by heat when a heat curing agent is not presentor by light when a photocuring agent is not present. Thus, unsaturatedepoxy resins can be both employed as the thermosetting resins in thesurface layers (2) used in this invention or as photopolymerizableresins in the interlayer (1) of this invention, their utility lying inthe presence therewith of an appropriate heat curing agent orphotocuring agent depending upon the positioning thereof in the sheetmolding material of this invention.

Heat curing agents which can be used in the surface layers (2) of thesheet molding material of this invention are compounds which initiatereaction by heating, and cure the thermosetting resin present. Asuitable amount of the heat curing agent will vary depending upon theproperties, reactivity, ability to produce the desired cured polymer,etc. An appropriate amount of the heat curing agent can be easilydetermined by routine testing. In general, a suitable amount of organicperoxide type heat curing agents ranges from about 0.01 to 5 parts byweight per 100 parts by weight of the thermosetting resin and a suitableamount of the heat curing agent for epoxy resins ranges from about 1 toabout 50 parts by weight per 100 parts by weight of the thermosettingresin. Specific examples of suitable heat curing agents which can beused in the surface layers are various organic peroxides, as radicalgenerators, such as benzoyl peroxide, lauroyl peroxide, acetyl peroxide,methyl ethyl ketone peroxide, cyclohexanone peroxide, t-butylhydroperoxide, p-menthane hydroperoxide, cumene hydroperoxide,di-t-butyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butyl perbenzoate, t-butyl peracetate and di-t-butylperphthalate; azobisisobutyronitrile; curing agents for epoxy resinssuch as diethylene triamine, triethylene tetramine, benzyl methyl amine,tris(dimethylaminomethyl)phenol, meta-phenylenediamine,diaminodiphenylmethane, diaminodiphenylsulfone, dicyandiamide, borontrifluoride monoethylamine, menthandiamine, phthalic anhydride, maleicanhydride, hexahydrophthalic anhydride, Nadic Methyl Anhydride(trademark of Allied Chemical formethylbicyclo[2,2,1]heptene-2,3-dicarboxylic anhydride), pyromelliticanhydride, chlorendic anhydride; and curing agents for phenolic resinsor melamine resins, such as hexamethylene tetramine, zinc sulfate,α,α'-dichlorohydrin, sodium bisulfate, dimethyl oxalate, ethylaminehydrochloride, triethylamine, formic acid, p-toluenesulfonic acid, boricacid, and calcium hydroxide. These heat curing agents may be usedindividually or as mixtures of two or more thereof. Suitable combinationof these heat curing agents can be selected depending on the type ofthermosetting resin.

A suitable amount of the heat curing agent is at least about 0.01 partby weight, preferably 0.1 to 5 parts by weight, per 100 parts by weightof the thermosetting resin. A heat curing agent for epoxy resins maysometimes be added in an amount of as large as 50 parts by weight per100 parts by weight of the epoxy resin. Thus, the amount of the heatcuring agent cannot be set forth unequivocally since such will bedependent on the nature of the thermosetting resin employed.

The desired properties of the sheet, such as fire retardancy, thermalstability, mechanical strength, electrical characteristics, low cost,and aesthetic appearance, can be met by appropriately choosing thecomposition of the resin containing the short fiber material orinorganic filler.

The term "irradiation with light" as used in the description of thisinvention denotes irradiation with light having a wavelength of about200 mμ to about 800 mμ. Suitable light sources which can be usedinclude, for example, sunlight, a xenon lamp, a carbon arc, a metalhalide lamp, a chemical lamp, a high pressure mercury lamp, and asuperhigh pressure mercury lamp. A high pressure mercury lamp and achemical lamp are preferred as the light source.

A suitable amount of irradiation with light will be dependent upon thecompositon of the interlayer (1), the kind of photocuring agentemployed, the thickness of the sheet molding material, whether theirradiation is prior to providing the surface layer (2), etc. The amountof the irradiation which is necessary can be easily determined byroutine testing.

The flow of the sheet molding material comprising the interlayer (1)cured by irradiation with light and both uncured surface layers (2) isinhibited under pressure and heat in the subsequent molding step becuasethe interlayer (1) has been cured to some extent. Even when the surfacelayers (2) flow, the thickness of the interlayer (1) is retained. Inthis way, press-forming can be conducted without using a mold, a spacer,etc., and, therefore, the resulting sheet molding material has superiormulti-stage press-formability.

The flowability of the interlayer (1) at the time of press-forming isdetermined mainly by the degree of curing of the interlayer (1). Thedegree of curing of the interlayer (1) can be controlled as desired byappropriately selecting a suitable light irradiation time with regard tothe photocuring agent used and the photopolymerizable resin used. Inother words, control of flowability is very easy, and accurate. Thethickness of the interlayer (1) and the surface layers (2) of the sheetmolding material of the present invention will be dependent upon theultimate end use desired. Thus, where an interlayer of a thickness ofabout 1 to about 5 mm is employed and the surface layers (2) have athickness of about 0.1 to 0.3 mm, the flowability resulting of the sheetmolding material of this invention is substantially the same as that ofthe interlayer (1) less any minor contribution of flowability due to thesurface layers (2). Where a sheet molding material of this inventioncomprises an interlayer of a thickness of about 0.5 mm with surfacelayers (2) a thickness of about 1 mm, the flow ratio or flowability willbe larger since the surface layers (2) are not cured, even though theinterlayer is photocured. Flowability of the sheet molding material ofthe present invention can be expressed by the flow ratio defined below.##EQU1##

A preferred flow ratio is about 0.5 to about 10%. If the flow ratio istoo low, the surface condition of the molded article obtained is poor,and the appearance of the article is unsatisfactory for marketing. Onthe other hand, if the flow ratio is too high, the unit cost ofproduction is high, and extra work is required for removing the flash.Furthermore, when resin which has flowed adheres to the surface of thepress, work to remove it is necessary. Hence, the productivity isreduced. Furthermore, when a different kind of a thin film is to belaminated to the surface layer(s) of the sheet molding material, creasesand distortion may occur in the thin film. If the flow ratio is toohigh, the desired thickness accuracy cannot be obtained, andunacceptable products are formed. Accordingly, easy and accurate controlof the flow ratio is an essential condition for increasing workingefficiency in multi-stage press-forming, and obtaining a sheet having agood thickness accuracy.

The uncured surface layers (2) flow at the time of press-formation, andthe heat curing agent acts for the first time during the press-formingto cure the thermosetting resin in the surface layers (2). These surfacelayers (2) are essential as layers which impart or increase adhesivestrength at the time of laminating a different kind of a thin film tothe surface layer(s) of the sheet molding material. If a suitablethermosetting resin composition is used, there is no need to use anadhesive between the surface of the sheet molding material and thedifferent thin film. These surface layers are also necessary since whenflow occurs, the surface can be smoothened. When these surface layersare made of a thermosetting resin which is non-tacky at room temperature(e.g., about 10°-30° C.), a different kind of thin film which is notself-supporting can be laminated uniformly to the surface layer(s) ofthe sheet molding material without creases occurring, and a sheetmolding material having very good storability and handleability can beobtained.

A suitable thickness for the surface layers (2) which can be employed inthis invention, while not limiting, generally ranges from about 0.01 mmto about 2 mm, preferably 0.05 to 0.5 mm.

The term "uncured state" as used in the description of the presentinvention denotes a state where no curing has occurred or a state wherecuring has occurred to a very low degree, e.g., 10% or less.Specifically, an "uncured" layer is soluble in at least one of dioxane,chloroform and tetrahydrofuran, e.g., to the extent no substantiallyinsoluble materials can be detected at room temperature.

As stated hereinabove, the flow ratio in the sheet molding material ofthis invention can be controlled by adjusting the degree of curing andthe thickness of the uncured surface layers (2) on the basis of thecombination of the cured interlayer (1) and the uncured surface layers(2), and a sheet having a good thickness accuracy can be obtained. Thelamination of a different kind of thin film to the sheet moldingmaterial of this invention can be accomplished easily and the sheetmolding material of this invention is especially suitable formulti-stage press-forming.

When a different kind of thin film is to be laminated to only onesurface (2) of the sheet molding material, the other surface layer (2)may also contain a photocuring agent and a photopolymerizable resin,e.g., as described above for the interlayer (1), thereby to form a sheetmolding material in which only that surface layer (2) to which thedifferent film has been laminated is maintained in an uncured state.Since one surface layer (2) is photocured in this case, the sheetmolding material is easy to handle, and has the advantage that use of areleasing sheet is not required on the cured surface layer (2). Asuitable amount of the photopolymerizable resin which can be present inthe surface layers (2) described above ranges from about 1 to 99% byweight of the photopolymerizable resin and about 0.01 to 1% by weight ofthe photocuring agent, each based on the total weight of thecompositions for the surface layer (2).

The sheet molding material in accordance with this invention in whichthe interlayer (1) contains a photocuring agent but does not contain aheat curing agent has additional superior advantages. Specifically,since the interlayer (1) does not contain a heat curing agent and, thus,is stable to heat, all methods of molding utilizing heat can be used.

Press-forming, extrusion, and calendering can be utilized inconventional sheet molding processes. However, only a press-formingmethod has been employed with thermosetting resins, because conventionalthermosetting resins contain a heat curing agent. Therefore, when anextrusion method or a calendering method, which is a continuous moldingmethod utilizing heat, is employed, the thermosetting resins cure duringthe processing and the operation must be stopped halfways. Inparticular, sheets having a thickness of about 1 to 2 mm and a width ofabout 1,000 mm have never been produced commercially by the extrusionprocess using thermosetting resins. The present invention has overcomethis drawback, and has made it possible to produce thermosetting resinsheet molding materials continuously using a sheet die and an extruderas in the case of thermoplastic resins. A suitable temperature at whichthe curing of the thermosetting resin present in the surface layers (2)of the embodiments of this invention can be accomplished ranges fromabout 50° to about 200° C., preferably 120° to 180° C.

Thus, the present invention also provides a process for continuouslyproducing a sheet molding material, which comprises extruding aninterlayer (1) as a sheet-like material using an extruder and a sheetdie, adhering a separately prepared surface layer (2) to both surfacesof the interlayer (1), and irradiating the resulting assembly withlight. The invention also provides a modification of the above processin which the interlayer (1) does not contain a heat curing agent but acontinuous-phase base material is included in the two surface layers(2). Since the interlayer (1) does not contain a heat curing agent, theinterlayer (1) is stable to heat. Hence, there is no likelihood ofcuring the interlayer (1) during the extrusion, and even when theprocess is operated for long periods of time, a molded sheet having agood thickness accuracy can be obtained in a stable manner and with highproductivity. By adhering a thermosetting resin surface layer (2)containing a heat curing agent to both surfaces of the resultinginterlayer (1), the sheet molding material of this invention can beobtained continuously. By irradiating both surfaces of the assembly withlight, a sheet molding material where only the interlayer (1) has beencured can be obtained.

The sheet molding material may be cut to the desired size prior tosubjecting the sheet molding material to multi-stage press-forming.Further, by directly passing the sheet molding material through, forexample, a double steel belt press, and curing the sheet moldingmaterial after, if desired, a different kind of thin film is applied tothe sheet molding material, a flat plate of thermosetting resin whichhas a very good thickness accuracy can be produced. This method islabor-saving, and has unprecedented high productivity.

The interlayer (1) of the sheet molding material of the invention isdesirably solid at room temperature. The composition for the interlayer(1) is kneaded, and then granulated or pelletized before extrusion.Extrusion can be performed using an ordinary monoaxial or biaxialextruder. The temperature should be preset at a point at which thecomposition for the interlayer (1) has a viscosity which permits theeasiest extrusion. Usually, a suitable temperature is about 50° to 140°C., and should be as low as possible. A suitable viscosity which permitseasy extrusion will range from about 10³ to about 10⁶ poise, preferably10⁴ to 10⁵ poise, at the temperature of extrusion.

The surface layer (2) which can be most suitably employed in this methodis a material obtained by impregnating a continuous-phase base materialwith a thermosetting resin which is non-tacky at room temperature. Theimpregnated material can be applied continuously to both surfaces of acontinuously extruded interlayer (1), e.g., by using pinch rolls. Inparticular, continuous-phase base materials of the glass fiber typeinhibit transmission of light only to a small extent, and can be sent toa successive light irradiating step.

In this case, too, when a photocuring agent and a photopolymerizableresin are added to one surface layer (2), a sheet molding material inwhich only one surface layer (2), is in an uncured state can beobtained.

When the resin composition of the interlayer (1) does not contain a heatcuring agent, the resin composition is a composition which contains aphotocuring agent and a photopolymerizable resin and, as optionalcomponents, a short fiber material, an inorganic filler and otheradditives. The combination of these components must be appropriatelyselected from those exemplified above. For example, a combination ofcomponents which will be cured during extrusion molding cannot be usedfor the interlayer (1). If a certain resin composition composed of acombination of a photocuring agent and a photopolymerizable resin istested at 60 rpm and 160° C. by a Brabender Roller Mixer and does notcure within a period of at least 1.5 hours, preferably at least 2 hours,the resin composition of the interlayer (1) can be extrusion-moldedsufficiently at least at about 120° C. or less.

Compositions which can actually be used in extrusion molding preferablycontain photocuring agents of the benzoin, benzophenone andanthraquinone types. Specific examples of these types of photocuringagents include benzoin methyl ether, benzoin ethyl ether, benzoinisopropyl ether, benzoin butyl ether, benzophenone,4,4'-bis(dimethylamino)benzophenone, 4,4'-bis(diethylamino)benzophenone,anthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone,2-t-butylanthraquinone, and 1-chloroanthraquinone. Preferredphotopolymerizable resins are combinations of unsaturated polyesterprepolymers or diallyl phthalate prepolymer with dimethyl fumarate,vinyl toluene, diallyl phthalate, diallyl maleate or triallyl cyanurate.Generally, compounds containing an acryloyl or methacryloyl group tendto be cured by the heat encountered during extrusion molding, e.g., dueto a temperature of above 120° C., and can be added to the resincomposition only in an amount of about 5% by weight or less. However,compounds having a high molecular weight per acryloyl or methacryloylgroup, such as polyethylene glycol diacrylate or dimethacrylate with adegree of polymerization n of n≧6 can be used in an amount of more thanabout 5% by weight whether they are monomers, or prepolymers (forexample, unsaturated epoxy resins, unsaturated polyurethanes,unsaturated polyamides, etc.).

When the extrusion molding is carried out at a temperature of as low asabout 60° C., the likelihood of heat curing can be reduced. Hence,usable resin compositions for the interlayer (1) can be screened byperforming the Brabender test described above at a temperature of 120°C., and the range of selection of the resin composition for theinterlayer (1) can be broadened.

In another embodiment, the invention also provides a sheet moldingmaterial with surface layers (2) containing a continuous-phase basematerial. The continuous-phase base material should not impair thetransmission of light when the surface layers (2) are first adhered tothe interlayer (1) and then the resulting assembly is irradiated withlight. However, when the interlayer (1) is first photocured and then thesurface layers (2) are adhered, all kinds of base materials, i.e.,transparent and opaque, can be used. Those continuous-phase basematerials which can generally be used in the invention are, for example,glass cloth, non-woven glass cloth, glass paper, paper, asbestos paper,papers formed from a mixture of cellulose and other fibrous material,synthetic fiber cloth, synthetic fiber non-woven cloth, syntheticpaper-like sheets, glass mats, felts, and nets. In particular, wovencloths of glass fibers are superior because they have high rigidity andimproved dimensional stability to warping, twisting and temperaturechanges when they are formed into a large-size flat plate. Papers areinexpensive, and most suitable for reducing the cost of the sheetmolding material. In this way, continuous-phase base materials ofdifferent kinds can be selected depending on the desired purpose. Athermosetting resin layer containing a continuous-phase base material isprepared by coating a thermosetting resin containing a heat curing agenton the continuous-phase base material, or melting and impregnating thethermosetting resin in the continuous-phase base material, orimpregnating the continuous-phase base material with a solution of thethermosetting resin and removing the solvent by drying. The sheetmolding material of the invention can be produced by adhering theresulting resin layer to both surfaces of the interlayer (1). The sheetmolding material containing a continuous-phase base material in thesurface layers (2) thereof produced in this manner has improved flexuralmodulus and dimensional stability, can be easily handled, and permitsincreased operating efficiency. When this type of sheet molding materialis formed into a thin large-size flat plate, a marked prevention ofwarping or twisting is achieved.

In an even further embodiment, the invention also provides a sheetmolding material having a metal layer laminated on at least one of thesurface layers (2). Metals which can be used in this embodiment includecopper, aluminum, nickel and silver, and of these metals, copper ispreferred. The thickness of the metal layer is not limited but generallyranges from 5 to 70 μm. The metal layer can be laminated on the sheetmolding material in a conventional manner.

The sheet molding material described hereinabove can be produced, forexample, by the following method.

A photopolymerizable resin containing a photocuring agent is kneaded,optionally together with a thermosetting resin containing a heat curingagent, a short fiber material, an inorganic filler, a viscositystabilizer, a pigment and other additives, and the mixture is formedinto an interlayer sheet using, for example, a press-forming method, acasting method, a roll method, etc.

Then, a thermosetting resin containing a heat curing agent is mixed,optionally with a short fiber material, an inorganic filler and otheradditives, and the resulting mixture is formed into a sheet by similarmeans. The surface layer sheet thus produced is adhered to both surfacesof the interlayer sheet produced earlier. At this time, one of thesurface layers may, if desired, contain a photopolymerizable resincontaining a photocuring agent.

Both surfaces of the resulting three-layer sheet molding material areirradiated with light to cure the interlayer (1) containing aphotocuring agent and a photopolymerizable resin.

Alternatively, the interlayer (1) may be first irradiated with lightprior to adhering the surface layers (2), and then both surface layers(2) may be adhered to the cured interlayer (1). This method isespecially advantageous when the interlayer (1) is to be made of aliquid resin because light irradiation can be used to produce a solidinterlayer sheet that is easy to handle, as stated hereinabove.

When the interlayer (1) is non-tacky at room temperature, the surfacelayers (2) can be obtained by merely coating the interlayer (1) withoutforming sheets of the composition for the surface layer (2).Particularly, a sheet obtained by curing the interlayer (1) byirradiation with light can be coated with a liquid thermosetting resincontaining a heat curing agent, or a solvent solution of thethermosetting resin and the heat curing agent followed by removing thesolvent, thereby to form an uncured surface layer (2) on both surfacesof the interlayer (1).

Since different kinds of film have good adhesion to the sheet moldingmaterials obtained by the present invention, the sheet molding materialsare suitable for multi-stage press-forming without using a special moldor a spacer, and can be used to produce sheets having a good thicknessaccuracy. The sheet molding materials of this invention are useful forvarious panels or boards, decorative sheets, electric insulation sheets,laminated sheets, and printed circuit base boards.

The following Examples are given to illustrate the present inventionmore specifically. However, it should be understood that the inventionis in no way limited by these Examples. All parts and percentages inthese Examples are by weight.

EXAMPLE 1

(a) A composition, non-tacky at room temperature, was prepared byblending 100 parts of an unsaturated polyester prepolymer having adegree of condensation of 40 obtained from a mixture of dimethylterephthalate and maleic anhydride (50:50 mol%) and ethylene glycol, 30parts of vinyltoluene, 65 parts of calcium carbonate and, as aphotocuring agent, 1 part of benzoin ethyl ether. The composition waspress-formed at 90° C. using a spacer to produce a plate having a sizeof 20 cm×20 cm with a thickness of 2 mm.

(b) Fifty parts of an unsaturated polyester resin composition asdescribed above but which did not contain benzoin ethyl ether, butrather as a heat curing agent, 2 parts of dicumyl peroxide, wasdissolved in 150 parts of chloroform to form a dope. A glass clothhaving a basis weight of 110 g/m² was immersed in the resulting dope.The chloroform was evaporated to form a heat curing agent andthermosetting resin-containing layer. The thickness of the glass clothin the layer was 150μ, and the thickness of the glass cloth afterimpregnation was 370μ. The resin pick-up was 250 g/m².

(c) The resin-impregnated glass cloth produced in (b) above was adheredto both surfaces of the plate produced in (a) above (with a size of 0.2cm×20 cm×20 cm) using a press-forming machine at 90° C. to form a sheetmolding material.

The sheet molding material was irradiated for 2 minutes with light froma superhigh pressure mercury lamp disposed at a distance of 30 cm fromthe sheet molding material. An uncured layer having a thickness of about300μ was present on both surfaces of the cured interlayer. (This wasexamined by immersing the sheet molding material thus-obtained inchloroform to dissolve the uncured layers.)

(d) The photocured sheet molding material was cured by pressing it at 50kg/cm² and 160° C. for 30 minutes using a press-forming machine withoutusing a spacer.

(e) As a comparison, a similar sheet molding material was prepared butin which the interlayer did not contain benzoin ethyl ether, and thenheat cured.

The results obtained for the sheet molding material and the comparativesheet molding material are tabulated below.

    ______________________________________                                                       Example 1 Comparison                                           ______________________________________                                        Thickness before 2.6         2.6                                              Molding (mm)                                                                  Thickness after  2.5         1.7                                              Molding (mm)                                                                  Thickness Accuracy*                                                                            0.1         0.8                                              after Molding (mm)                                                            Flow Ratio (%)   4           30                                               ______________________________________                                         *The thickness accuracy is the value obtained by subtracting the minimum      thickness of the molded material from the maximum thickness of the molded     material.                                                                

EXAMPLE 2

(a) A liquid composition of 60 parts of an unsaturated polyesterprepolymer having a molecular weight of about 2,000 obtained bycondensing o-phthalic acid (50 mol%), maleic anhydride (50 mol%) andpropylene glycol (102 mol%) (Polylite FH-103, a trademark of JapanReichhold Chemical Inc.), 40 parts of styrene and, as a photocuringagent, 1 part of 2-ethylanthraquinone, was poured to a thickness of 3 mmbetween two glass plates having a size of 25 cm×25 cm with a glasschopped strand mat (400 g/m²) interposed between the glass plates. Theresulting assembly was then irradiated for 1 min. with light from asuperhigh pressure mercury lamp disposed 30 cm away from the assembly.

(b) Separately, 50 parts of a 40:60 by weight mixture of abisphenol-type unsaturated polyester prepolymer (ATLAC 382 A, atrademark of ATLAS, comprising the reaction product of bisphenol A,propylene glycol and fumaric acid; mol. wt.: about 2,500) and anunsaturated epoxy resin (a dimethacrylate-terminated bisphenol-typeepoxy resin having an epoxy value of 450), 1 part of di-t-butylperoxide, as a heat curing agent, and 50 parts of kaolin were dissolvedin 100 parts of methyl ethyl ketone. The resulting solution was coatedon both surfaces of the photocured sheet obtained as described in (a)above, and the solvent was removed by drying. The coated surface layerhad a thickness of 0.2 mm.

(c) The resulting sheet molding material was pressed for 20 minutesusing a press-forming machine at 170° C. and 30 kg/cm² without using aspacer. The resulting cured sheet had a thickness of 3.2 mm, a thicknessaccuracy of 0.1 mm, and a flow ratio of 5%.

EXAMPLE 3

(a) Fifty parts of a diallyl phthalate prepolymer having an iodine valueof 60, 5 parts of diallyl phthalate monomer, 2.5 parts oftrimethylolpropane triacrylate, 0.5 part of benzophenone, as aphotocuring agent, 100 parts of aluminum hydroxide and 25 parts ofpolyvinyl alcohol staple fibers were kneaded using a mixing roll, andthe mixture was formed by a press into a sheet having a thickness of 3.5mm and a size of 30×30 cm.

(b) Then, 50 parts of the diallyl phthalate prepolymer as describedabove, 7.5 parts of diallyl phthalate monomer and 1 part of methyl ethylketone peroxide as a heat curing agent were dissolved in 100 parts ofacetone. A polyester non-woven fabric (70 g/m²) was impregnated withthis solution and dried to remove the acetone. The resulting impregnatedsheet was adhered to both surfaces of the press-formed sheet produced asdescribed in (a) above to obtain a sheet molding material.

(c) Both surfaces of the sheet molding material were irradiated for 2minutes with light from a xenon lamp positioned 20 cm away from thesheet molding material. Each of the surface layers had a thickness ofabout 0.4 mm.

(d) The sheet material was press-formed for 20 minutes at 160° C. and 75kg/cm² without using a spacer. The resulting cured sheet had a thicknessof 4.5 mm, a thickness accuracy of 0.15 mm and a flow rate of 7%.

EXAMPLE 4

(a) A sheet having a thickness of 1.5 mm and a size of 20×20 cm wasprepared using 100 parts of an unsaturated epoxy resin obtained from abisphenol A-type epoxy resin having an epoxy rquivalent of 900 and 1.5mols, per mol of the epoxy resin, of acrylic acid, 20 parts of NadicMethyl Anhydride, as a heat curing agent, and 2 parts of benzoin methylether, as a photocuring agent.

(b) Separately, 100 parts of a bisphenol A-type epoxy resin having anepoxy equivalent of 500 and 3 parts of dicyandiamide, as a heat curingagent, were dissolved in a mixture of 150 parts of methyl ethyl ketoneand 50 parts of dimethylformamide. A glass cloth (203 g/m²) wasimpregnated with the solution and dried to remove the solvent (the resinpick-up was 110 g/m²).

(c) The resulting impregnated glass cloth produced in (b) above wasadhered to both surfaces of the sheet produced in (a) above. Eachsurface of the assembly was irradiated for 1 minute with light from asuperhigh pressure mercury lamp disposed 5 cm away from the sheetmolding material.

(d) The resulting sheet molding material had an uncured layer having athickness of 0.3 mm on both surfaces thereof. When the sheet moldingmaterial was press-formed for 1 hour at 180° C. and 100 kg/cm² withoutusing a spacer, the product obtained had a thickness of 1.65 mm, athickness accuracy of 0.05 and a flow ratio of 3%.

EXAMPLE 5

(a) A composition of 100 parts of an unsaturated polyester prepolymer(ATLAC 363 E, a trademark of ATLAS, reaction product of bisphenol A,ethylene glycol, fumaric acid+ unidentified glycol; mol. wt. about3,000), 10 parts of 1,4-butanediol diacrylate, 100 parts of bisphenolA-type epoxy resin (epoxy equivalent: 900), 5 parts of a borontrifluoridemonoethylamine complex, as a heat curing agent, 2 parts ofbenzoin butyl ether as a photocuring agent, 200 parts of silica powder,and 20 parts of chopped strand glass fibers (3 mm) was kneaded for 20minutes in a kneader at 100° C. The mixture was then formed with apress-forming machine at 100° C. using a spacer into a sheet having athickness of 2 mm and a size of 20 cm×20 cm.

(b) Separately, 30 parts of the unsaturated polyester prepolymerdescribed in (a) above, 70 parts of an unsaturated epoxy resin (adiacrylate of fire retardant epoxy resin, AER 714, a product of AsahiChemical Ind., Co., Ltd.; epoxy equivalent: 600) and 2 parts of2,5-dimethyl-2,5-di(t-butylperoxy)hexane, as a heat curing agent, weredissolved in 150 parts of methyl ethyl ketone. A glass cloth (125 g/m²)was impregnated with the solution and dried in an oven at 80° C. (resinpick-up: 100 g/m²).

(c) Additionally, 1 part of benzoin butyl ether was added as aphotocuring agent to the methyl ethyl ketone solution described above.An impregnated glass cloth was prepared in a similar manner as describedabove using this solution.

(d) The two types of glass cloths produced in (b) and (c) above wereadhered to both surfaces of the above sheet by a press at 100° C.

(e) For comparison, a sheet molding material having a photocuringagent-containing resin impregnated glass cloth adhered to both surfacesof the above sheet was prepared.

(f) Each of the two sheet molding materials was irradiated for 5 minuteswith light from chemical lamps disposed 5 cm away from both surfaces.

The sheet molding material in accordance with this invention had anuncured layer having a thickness of 0.2 mm. The sheet for comparison didnot contain an uncured layer.

(g) A copper foil was superimposed on each of the sheet moldingmaterials (in the case of the sheet molding material in accordance withthis invention, the copper foil was superimposed on the uncured surfacelayer), and press-formed for 30 minutes at 170° C. and 30 kg/cm² withoutusing a spacer.

The copper-clad laminated sheets had the properties tabulated below.

    ______________________________________                                        Properties       Example 5  Comparison                                        ______________________________________                                        Thickness of Uncured Surface                                                                   0.2        0                                                 Layer (mm)                                                                    Thickness of Material before                                                                   2.4        2.4                                               Curing (mm)                                                                   Thickness after Curing (mm)                                                                    2.3        2.4                                               Thickness Accuracy (mm)                                                                         0.05      0.1                                               Flow Ratio (%)   2.0        <0.5                                              Flexural Modulus (kg/mm.sup.2)*                                                                2540       2710                                              Flexural Strength (kg/mm.sup.2)*                                                               22.1       22.4                                              Insulation Resistance*                                                        Normal Conditions (ohms)                                                                       1 × 10.sup.15                                                                      1 × 10.sup.15                               After Boiling (ohms)                                                                           6 × 10.sup.11                                                                      7 × 10.sup.11                               Copper Foil Delamination                                                                       2.2        0.4                                               Strength (kg/cm)*                                                             Solder Heat Resistance                                                                         85         7                                                 (sec)*                                                                        ______________________________________                                         *JIS C6481                                                               

It can be seen from these results that the product of this Example had ahigher copper foil delamination strength and far higher solder heatresistance than the product for comparison.

EXAMPLE 6

(a) Twenty parts of an unsaturated polyester prepolymer as described in(a) of Example 1, 3 parts of diallyl phthalate, 2 parts ofpentaerythritol tetraacrylate, 0.4 parts of benzoin isopropyl ether, asa photocuring agent, 5 parts of powdered polyethylene, 55 parts ofcalcium silicate, and 15 parts of glass chopped strands (6 mm) wereblended, and kneaded at 90° C. in a biaxial extruder to pelletize themixture.

A coat hanger-type sheet die having a width of 350 mm was fitted to a30φ monoaxial extruder, and the pellets were extruded continuously intoa sheet having a thickness of 2 mm under the following conditions.

Barrel Temperature: 90° C.

Die Temperature: 92° C.

Pressure: 110 kg/cm²

Rate of Extrusion: 12 kg/hr

(b) Separately, 20 parts of the same unsaturated polyester prepolymer asdescribed in (a) of Example 1, 5 parts of diallyl phthalate and 0.5 partof cumene hydroperoxide, as of heat curing agent, were dissolved in 30parts of dioxane. A glass cloth (203 g/m²) was impregnated with thissolution to form an impregnated glass cloth having a thickness of 0.3 mmand a resin pick-up of 115 g/m².

(c) The impregnated glass cloth was adhered to both surfaces of theextrusion-molded sheet obtained as described above using a pair of pinchrolls provided at the exit of the sheet die, and thus, a sheet moldingmaterial was continuously produced.

The sheet molding material was subsequently passed through a pair ofhigh pressure mercury lamps disposed vertically, and irradiated withlight with the distance between each surface of the material and eachmercury lamp being maintained at 20 cm. The irradiation width of thehigh pressure mercury lamp was 20 cm, and the rate of sheet travel was15 cm/min. The resulting sheet molding material had a 0.3 mm thickuncured layer on both surfaces thereof, and a thickness of 2.55 mm±0.005mm.

After operating the machine continuously for 8 hours, the joint portionbetween the extruder and the die attained a temperature of 120° C., butthis caused no inconvenience in the operation.

(d) The sheet molding material was cut to a length of 35 cm, and the cutpiece was press-formed for 30 minutes at 150° C. and 75 kg/cm² withoutusing a spacer. The press-formed sheet had a flow ratio of 2%, and aftercuring had a thickness of 2.5 mm±0.03 mm.

(e) For comparison, 0.1 part of cumene hydroperoxide as a heat curingagent was added to the resin composition described in (a) above for aninterlayer, and the resulting composition was extruded under the sameconditions as described above. In 2 hours, the composition cured, andcould not be extruded further.

EXAMPLE 7

(a) A powdery mixture of 10.5 parts of an unsaturated polyesterprepolymer having a degree of condensation of 38 obtained by reactingequimolar amount of a mixture (50:50 mol%) of dimethyl terephthalate andfumaric acid and a mixture (90:10 mol%) of ethylene glycol and propyleneglycol, 3 parts of diallyl phthalate monomer, 12 parts of a half esterof methacrylic acid and a fire retardant epoxy resin (AER 714, a productof Asahi Chemical Ind. Co. Ltd., epoxy equivalent: 600; bromine content:24 wt%), 0.4 part of benzoin ethyl ether, as a photocuring agent, 4.5parts of polypropylene powder (passing 50 mesh, Flowblen B-200, a tradename of Seitetsu Chem. Ind.), 60 parts of heat treated aluminumhydroxide described in Example 2 of Japanese Patent Application (OPI)No. 133339/76, 10 parts of chopped glass strands (3 mm), and 1 part ofantimony trioxide (particle size: about 0.2 to 5μ) was mixed in a mixer.A strand die and a hot cutter were secured to the end of a biaxialextruder, and the resulting mixture was kneaded in the extruder at 95°C. at an extrusion rate of 200 kg/hr to form pellets.

A coat hanger-type sheet die having a width of 1,200 mm was fitted to a90φ monoaxial extruder, and the pellets were extruded into a sheethaving a thickness of 1.3 mm and a width of 1,185 mm under the followingconditions.

Temperature of Resin Extruded: 105° C.

Pressure at Inlet of Die: 75 kg/cm²

Rate of Extrusion: 180 kg/hr

Speed of Sheet: 1.3 m/min

(b) Separately, 30 parts of a bisphenol-type unsaturated polyesterprepolymer (ATLAC 363E, a trademark of ATLAS, reaction product ofbisphenol A, ethylene glycol, fumaric acid+unidentified glycol; mol.wt.: about 3,000), 70 parts of the half methacrylate of a fire retardantepoxy resin described in (a) above, and, as a heat curing agent, 1.5parts of dicumyl peroxide and 2 parts of a borontrifluoridemonoethylamine complex were dissolved in 80 parts of tolueneand 20 parts of methyl ethyl ketone. A glass cloth (203 g/m²) wasimpregnated with the resulting solution and dried to remove the solvent.The resulting impregnated glass cloth having a resin pick-up of 110 g/m²was taken up.

(c) The impregnated glass cloth was adhered to both surfaces of thesheet produced in (a) by pinching it with a pair of 300φ cooling rollsat about 18° C. provided immediately rearward of the sheet die. Theresulting sheet molding material had a thickness of 1.7±0.1 mm.

The resulting sheet assembly was passed over a 5 m roller table to coolthe assembly to room temperature in the air. Then, the assembly waspassed between three pairs of high pressure mercury lamps (length 1400mm; 80 w/cm) while maintaining a distance of 300 mm from the lamps. Theresulting sheet molding material had a 0.2 mm-thick uncured layer onboth surfaces thereof.

(d) The sheet molding material was cut into a piece with a width of 1040mm and a length of 1060 mm. A 35 μ-thick copper foil was superimposed onone surface of the cut piece. Ten such assemblies were made one stage,and 20 such stages were press-formed by a 20-stage press-forming machineat 70 kg/cm².

In the press-forming process, the temperature was increased from roomtemperature to 160° C. over the course of 15 minutes, the material wasmaintained at 160° C. for 30 minutes, and then cooled to roomtemperature over the course of 15 minutes. The properties of theresulting copper-clad laminated plate were as follows:

    ______________________________________                                        Thickness and Accuracy (mm):                                                                         1.62 ± 0.02                                         Flow Ratio (%):        2                                                      Copper Foil Delamination:                                                                            1.8                                                    Strength (kg/cm)                                                              Solder Heat Resistance (sec):                                                                        93                                                     Heat Resistance (30 min.) (°C.):                                                              250                                                    Flexural Strength (kg/mm.sup.2):                                                                     28.2                                                   Warping (%):           1.1                                                    Twisting (%):          2.0                                                    Insulation Resistance (ohms):                                                                        3.5 × 10.sup.14                                  Dielectric Constant (1 MHz):                                                                         4.8                                                    Dielectric Loss Tangent (1 MHz):                                                                     0.024                                                  Arc Resistance (sec):  189                                                    ______________________________________                                    

EXAMPLE 8

(a) A sheet having a thickness of 1.3 mm was prepared from a compositioncomprising 20 parts of an unsaturated polyester prepolymer having amolecular weight of about 3,500 obtained from isophthalic acid (50mol%), maleic acid (50 mol%), propylene glycol (60 mol%) and neopentylglycol (40 mol%), 5 parts, of diallyl phthalate monomer, 4 parts ofmelamine resin, 0.1 part of hexamethylene tetramine, 10 parts of glassfibers (6 mm), 60 parts of an inorganic filler (obtained by heattreating aluminum hydroxide at 300° C. for 4 hours; as described inExample 3 of Japanese Patent Application (OPI) No. 133339/76), and 0.3part of benzoin ethyl ether.

(b) A glass cloth (203 g/m²) was impregnated with a resin solutioncomprising 30 parts of a diallyl isophthalate prepolymer having aniodine value of 90, 0.6 part of cyclohexanone peroxide and 70 parts ofmethyl ethyl ketone, and dried to remove the solvent to a pick-up of 120g/m².

(c) The impregnated glass cloth was adhered to both surfaces of thesheet produced as described in (a) above, and both surfaces of theassembly was irradiated for 3 minutes with light from six 20 W chemicallamps.

(d) The resulting sheet molding material had a 0.15 mm-thick uncuredlayer on both surfaces thereof with a photocured interlayer. The sheetmolding material was pressed for 20 minutes at 170° C. and 50 kg/cm² toform an electrical insulation sheet having a thickness of 1.6 mm. Theproperties of the electrical insulation sheet were as follows:

    ______________________________________                                        Thickness and Accuracy (mm):                                                                    1.59 ± 0.05                                              Flow Ratio (%):   1.5                                                         Flexural Strength (kg/mm.sup.2):                                                                32         JISC 6481                                        Insulation Resistance (ohms):                                                                              "                                                Normal Condition: 2 × 10.sup.15                                         After Boiling:    4 × 10.sup.11                                         Arc Resistance:   187                                                         Tracking Resistance (V):                                                                        500 OK     (IEC method)                                     Dielectric Break-down                                                         Voltage (KV/mm):  20         JISC 6481                                        Fire Retardancy:  94 V-0     (UL standard)                                    ______________________________________                                    

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A process for continuously producing a sheetmolding material comprising (1) an interlayer containing aphotopolymerizable resin and a photocuring agent for thephotopolymerizable resin and (2) a surface layer of a thermosettingresin containing a heat curing agent for the thermosetting resin on bothsurfaces of the interlayer (1), which comprisesextruding a compositioncontaining a photopolymerizable resin and a photocuring agent for thepolymerizable resin as the interlayer (1) using an extruder and a sheetdie, adhering a surface layer of a thermosetting resin containing a heatcuring agent for the thermosetting resin to both surfaces of theinterlayer (1) to form surface layers (2) thereon, and irradiating theassembly with light to cure the interlayer (1).
 2. The process of claim1, wherein the surface layer of the thermosetting resin containing aheat curing agent for the thermosetting resin adhered as one surfacelayer (2) additionally contains a photopolymerizable resin and aphotocuring agent for the photopolymerizable resin.
 3. The process ofclaim 1, wherein the composition for the interlayer (1) is free of aheat curing agent and both surface layers (2) contain a continuous-phasebase material.
 4. The process of claim 3, wherein the composition forthe interlayer (1) additionally contains at least one of a short fibermaterial and an inorganic filler.
 5. The process of claim 3, wherein thecontinuous-phase base material is a glass cloth.
 6. A process forcontinuously producing a metal-clad laminate comprising (1) aninterlayer containing a photopolymerizable resin and a photocuring agentfor the photopolymerizable resin, (2) a surface layer of a thermosettingresin containing a heat curing agent for the thermosetting resin on bothsurfaces of the interlayer (1), and (3) a metal layer on one surfacelayer (2), which process comprisesextruding a composition containing aphotopolymerizable resin and a photocuring agent for thephotopolymerizable resin as the interlayer (1) using an extruder and asheet die, adhering a surface layer of a thermosetting resin containinga heat curing agent for the thermosetting resin to both surfaces of theinterlayer (1) to form surface layers (2) thereon, irradiating theassembly with light to cure the interlayer (1), and laminating on atleast one of the surface layers (2) a metal layer (3).
 7. The process ofclaim 6, wherein the metal layer is a layer of copper.
 8. The process ofclaim 6, wherein the composition for the interlayer (1) is free of aheat curing agent and both surface layers (2) contain a continuous-phasebase material.
 9. The process of claim 8, wherein the composition forthe interlayer (1) additionally contains at least one of a short fibermaterial and an inorganic filler.
 10. The process of claim 8, whereinthe continuous-phase base material is a glass cloth.